When electromagnetic wave projects to an object/material, the electromagnetic way may interact with the object/material through absorption, reflection, refraction, interference, or scattering and then the interacted electromagnetic wave may carry information of the object. In addition, the electromagnetic wave may stimulate the objects or the materials to radiate electromagnetic wave. Owing to that, the physical or chemical information such as compositions, moisture content, color, size, or surface structure of the objects or the materials may be extracted out by analyzing the spectrum of the scattering or reflective electromagnetic wave from the objects or the materials.